Advice for parents is available from CEOP (The Child Exploitation and Online Protection Centre, run by the police) which offers these top tips:

Ask your children to show you the sites they use.
Ask your children to set their profile settings to private on social networking sites.
Ask your child about their online friends.
Set appropriate parental controls on your child’s computer, mobile and games console.
Encourage your child to let you know if they are worried about something online.

Make sure you know where to get help if you are concerned about your child - a list of services is available from www.ceop.police.uk/safety-centre.